This invention relates to an apparatus and a method for mounting and removing tyres on and from respective wheel rims.
As is known, apparatuses for mounting and removing tyres on and from respective wheel rims are equipped with a rim supporting element that is suitably power driven to turn the rim during mounting or removal of the tyre.
Usually, the rim supporting element is positioned with its axis vertical (that is, directed substantially in the direction of application of the weight force) or, alternatively, with the axis horizontal.
It should be noted that this invention relates to machines for mounting (and removing) the tyres, without any limitation as to the orientation of the supporting element.
For brevity and simplicity, however, this description will refer to the case where the supporting element is positioned with its axis vertical in such a way as to turn the wheel about a longitudinal axis of rotation oriented along said vertical axis.
Above the supporting element, there is a set of tools designed to position the tyre bead (that is, the annular edge of the tyre) at predetermined positions on the rim.
It should be noted that a tyre has two beads, corresponding to the two annular ends (or edges) of the tyre itself.
Each bead has a head portion, oriented radially, and a lateral portion.
Prior art tools for mounting and removing tyres on and from wheel rims include, for example, a shaped element (for mounting) and a lever or a claw (for removing) which are designed to be inserted between the bead and the rim in such a way as to position the bead at a predetermined position relative to the rim, in particular to push a first portion of the bead between the annular outer edges of the rim at a respective groove (during mounting) or to extract the bead from the rim and keep it in an extracted position relative to the rim groove (during removal).
Next, the rim is turned about its longitudinal axis so that the tool (which is held still while the rim is rotated) slides along at least a part of the circumference of the bead in such a way as to prise the entire bead inwards (during mounting) or outwards (during removal) over the edge of the rim.
In addition, during mounting, a pressure disc is used to push a side wall of the tyre towards the opposite side wall.
During removal, on the other hand, the pressure disc is used to detach the tyre bead from the rim (in effect, during use, the tyre becomes very hot, causing the rubber to vulcanize, thereby making the bead adhere to the wheel rim). The bead pressure disc, connected to one end of an operating arm, is therefore also known as bead loosener.
The pressure disc may also be used as a further aid during tyre mounting.
For example, when mounting the tyre on the rim, the pressure disc (or bead loosener) is usually used to facilitate correct positioning of the bead relative to the rim.
When mounting very rigid or large tyres, a pivoting clamp known by the trade name of “Tucano” is also used. This clamp also holds the tyre bead in place relative to the rim so as to minimize tension during mounting operations (that is, the mechanical strain the tyre bead is subjected to while it is being fitted to the wheel rim).
The clamp consists of a gripper designed to hold the edge of the rim at a zone of the rim where the bead has already been pushed onto the rim. Under the gripper there is a flat part that presses the side wall of the tyre near the bead. This flat part is pivotally mounted so that it remains in contact with the tyre as the latter moves.
It should be noted that the rim forms a first and a second seat (in the form of annular grooves) for receiving a first and a second bead during use of the wheel. The seats are located at opposite lateral ends of the rim.
The rim also has an annular groove or channel running round the middle of it.
This annular groove is in the form of a recess designed to receive at least one portion of the tyre bead temporarily during mounting operations.
In effect, at least during an initial stage of the mounting operation, the axis of the tyre is inclined with respect to the axis of the rim. In this situation, a first portion of the bead (or rather, of one of the two beads) is on the outside of the rim, held by the mounting/removal tool, while a second portion of the same bead (the portion diametrically opposite it) is inside the rim channel, allowing the tyre to be moved in a direction perpendicular to the rim axis, towards the mounting/removing tool.
This, as is known, facilitates tyre mounting by reducing the mechanical strain the bead is subjected to.
In light of the above, the engagement tool consisting of the above mentioned clamp is designed to push one side of the tyre, close to the bead, so as to keep the bead inside the channel in the zone of the bead diametrically opposite the portion of the bead that interacts with the mounting/removing tool.
The clamp is used together with a rim guard fitted to the edge of the rim to prevent damage to the bead as it moves over the sharp edges of the rim.
In effect, when mounting the tyre on the rim, the bead is subjected to mechanical strain that often leads to tyre damage. That is because the bead is subjected to radial strain (bead compression), axial strain (bead lifting) and tangential strain (bead pulling, due to the frictional component). All these types of mechanical strain on the bead, if they exceed certain limits (specified by tyre manufacturing associations and automobile constructors) may lead to serious tyre damage.
In this regard, it must be stressed that the risk of damage to the bead is particularly serious if it occurs during mounting because, once the tyre has been mounted, the damage, if any, is not visible before the tyre is used.
Further, the problem is felt particularly strongly on account of the use of run flat tyres, that is, tyres designed to resist the effects of deflation. Thus, in the event of a failure, a long time might pass before the driver realizes the tyre is damaged.
In fact, tyre manufacturers now tend to make tyres harder and with the shoulder lower down: this worsens the problem of damage to the tyre during mounting and removal.
To overcome this drawback, sensors such as extensometers applied to the tool or to the bead loosener are used, as is known from patent document IT1274552.
However, this solution does not allow accurate and reliable measurement of the mechanical strain the tyre bead is subjected to during mounting and removal.
In effect, the solution makes it possible to measure only the strain that results in deformation of the tool (that is, of the bead loosener). A great deal of the strain applied the bead is subjected to, however, is absorbed by the elasticity of the tool mounting structures. Moreover, the flexibility of the tools is limited and variable in time.
Another technical solution is known from patent document IT1263799.
This solution relates to a tyre removing machine comprising a pair of arms located on opposite sides of the wheel and movable towards each other to abut the sidewalls of the tyre so as to detach the bead from the rim (in practice, the arms are used as two bead looseners).
In this solution, the arms are equipped with sensors (torque meters in general, extensometers in particular designed to measure the pressure applied by the arms to the sides of the tyre).
The pressure applied by the arms, however, is not converted into or referable to mechanical strain acting on the bead.
This solution cannot therefore be used to obtain really useful and effective information on the mechanical strain applied to the bead and potentially able to damage the bead.
A further technical solution concerning an apparatus for servicing tired wheel for motor vehicles is already known from document EP1479538.
In this solution, the apparatus comprises a rotatable motor-driven support for the positioning of the tired wheel. The rotatable support is connected to the motor by a mechanical clutch which is used to disconnect the rotatable support from the motor, automatically and mechanically, when a critical load value, consisting of the mechanical strains applied to the tired wheel for assembling or disassembling it, is reached.
Moreover, this solution comprises an encoder designed to control the angular position of the rotatable support so that the encoder defines a position sensor directed to verify when the clutch is operative.
However, also this solution does not allow accurate and reliable measurement of the mechanical strains the tyre bead is subjected to during mounting and removal, nor allows the monitoring of the trend of said strains.